Process for the removal of metallic silver from photographic material

ABSTRACT

A process for removing metallic silver from photographic materials is provided, wherein any sparingly soluble silver salts present are not attacked. This process comprises treating the photographic material with an acid bath free from anions that form sparingly soluble silver salts and which bath contains an oxidant and a complexing agent. The oxidant has a standard redox potential of at most +0.8 Volts and the complexing agent has a silver complex stability constant of at most 109 (liter/mole)2. This process is of special importance in carrying out the silver dye bleach negative-positive process. The main advantage of the process is the fact that it uses only a small number of bathes and no strong oxidants.

United States Patent 1191 Meier 1 1 Feb; 13, 1973 1541 PROCESS FOR THE REMOVAL OF 2,699,394 1/1955 Gaspar .;...:.....96/99 METALLIC SILVER FROM PHOTOGRAPH: AL FOREIGN PATENTS OR APPLICATIONS [75] Inventor: Max Meier, pfi Switzerland 739,202 10/1955 Great Britain.' ..96 60 7 [731 Assignees Ciba-Geigy AG, Basle, Switzerland primary Examiner Travis Brown [22] Filed; July. 21 1970 Assistant Examiner-M. F. Kelley Attorney-Harry Goldsmith, Joseph G. Kolodny and 21 Appl. No.: 56,945 MarioA Monaco v [30] Foreign Application Priority Data [57] ABSTRACT July 30, 1969 Switzerland ..11605/69 A Process for removing metallic Silver from P graphic materials is provided, wherein any sparingly 52 Us. (:1 ..96/60 R, 96/53, 96/59 Soluble Silver Salts present are not attacked. This 511 Int. Cl. ..G03c 7/00, G036 5/50, G036 5/32 Pr comprises treating the photographic material [58] Field 61 Search ..96/20, 53,61,- 59, 60 with a acid bath free from that form sparingly 1 1 soluble silver salts and which bath contains an'oxidant [56] R fe Cit -d and a complexing agent. The oxidant has a standard redox potential of at most +0.8 Voltsand the com- UNITED STATES PATENTS plexing agent has a silver complex stability constant of 2,304,987 12/1942 Young; .Q ..96/60 109 (liter/mole)? This Process is 0f Special 2 74 0'0 5 95 portance in carrying out the silver dyebleach nega- 2,020,775 11/1935 Gaspar....= ..96/53 fi -p t p c s T m in ad n ge of the 2,113,329 1 4/1938 Mannes et al.. .....96/55 process is the fact that it uses only a small number of 2,322,001 6/1943 Ehrenfried ..96/53 bathes and no strong oxidants. 2,322,084 6/!943 Young, ..96/53 11/1950 Vittum ..96/60 9 Claims, No Drawings 1 PROCESS FOR THE REMOVAL OF METALLIC SILVER FROM PHOTOGRAPHIC MATERIAL The present invention relates to a process for removing metallic silver from photographic materials.

A number of processes are known forremoving silver and silver halides from photographic materials. The choice of'the process to be applied depends on the requirements of the individual photographic process.

,Thus, in -the conventional production of a silver image by developing exposed silver halide it is necessary to remove the residual, undeveloped silver halide, forexample by means of a solution of thiosulphate.

- In a direct positive development, on the other hand,-

the primarily developed silver must be removed without attacking any residual, undeveloped silver halide since in a further process step the latter is developed to the positive silver image. This can be done with oxidation baths which convert the silver into a soluble silver salt which can diffuse out of the photographic layer, for example, a sulphuric acid solution of potassium dichromate'orpotassium permanganate, for

which purpose the standard redox potential of these solutions must be greater than +0.8. Volt, which is the standard potential of Ag Ag". v

In other photographic processes, especially color I processes, both the silver and. any silverhalide must be removed; this can be done with so-called bleach fixing bathssthat contain an oxidant as well as a solvent for silver halide, for example Farmers reducer or bleach fixing baths, described in German specification No. .l ,l46,-36 3 and US. Pat. No. 2,748,000.

If desired, the oxidation of silver and .the washing out of the silver halide. may-be carried out in separate baths by first oxidizing the silver and then dissolving the silver halide. In this case oxidation of the silver may also be carried out with a solution that converts the silver into a sparingly soluble silver salt, forexample a hydrochlo-' ric acid solution of copper(ll)chlori de or a solution of potassium-iron(lll)cyanide since the sparingly soluble silver salts formed remain in the layer and are removed during the subsequent fixing operation.

For certain reversal processes, however, oxidation baths, such as dichromate-sulphuric acid, cannot be used since theseoxidants also decompose other componentspresent in thephotographic layer.

Thus, strong oxidants-cannot be used ina silver reversal development within the framework of the silver dye bleach-negative positive process since many of the azo dyestuffs used in this process may be destroyed by oxidation. While it is possiblejin such a case to adopt the procedure proposed in German specification No. l,l54,347, this process is cumbersome since it requires several additional treatment one emulsion layer, wherein the said material is treated with anacid bath which is free from anions that form sparingly soluble silver salts and contains 1. one or more oxidants having a standard redox potential ofat most-+0.8 ,Volt and;

2. a complexing agent having a silver complex stability constant of'at most l0 (liter/mole The standard'redox potential of the oxidant should husually be within the range from +0.15 to +0.8 Volt,

preferably from'+0.4 to +0.8 Volt. Suitable oxidants are copper(ll)salts or more especially quinones and iron(lll)salts. Particularly good resultsare obtained with iron(lll)salts, for example iron(lll)perchlorate,

iron(lll)nitrate or ammonium iron(lll) sulfate. According to this invention only anions that do not form sparingly soluble silver salts can be used. The oxidation potential of these oxidants must be below +0.8 Volt,

the oxidation potential of Ag Ag.

. The standard redox potential of the following elec rro-chemical reactions is, for example:

Fe e ,2 Fee +0.77-v olt Ca ce :2 011+ +0.17 volt Benzodulnone 211* 2e hydroquinone +0.7 volt Preferably used complexin'g'agents are those which display a silver complex stability constant of from 10" to 10 (liter/mole). Among the com plexing agents having a silver complex stability constant within this range are water-solubleunsaturated compounds,for example allyl alcohol,initriles, for example acetonitrile, certain heterocyclic amines, for example pyrazine, and thioethers' Especially suitable complexing agents are those having a silver complex stability constant of from 10 to 10 (liter/moleY, especially water-soluble thioethers, and preferably monothiosethers. Ofspecial:

value are water-soluble aliphatic monothioethers, which corresponds to the formula v I r'- r 2 2 inwhich R, and R, whichmay be the same or different each represent an alkyl group containing from one to threecarbon' atoms, and X and X each represent a hydrogen atom or a hydroxyl or carboxyl group.

Suitable water solublethioethers are, for example:

thiodiglycollic acid,

thiodipropionic acid,

'2 hyd'roxyethyl-methylsulphide thiodiglycol.

and

Apart from the aliphatic monothioethers of the formula l it is possible to use water-soluble thioethers in "which R and R are aromatic or heterocyclic residues, for example the disodium saltof di-(para-sulphophenyl)-sulphide, 'or the free acid thereof. Further suitable are cyclic water-soluble thioethers, 'such as thiophene- 2,5-dicarboxylic acids which correspond, for example, to the formula in which X, and X have the meanings defined above.

especially I Very weak complexing agents, such as allyl alcohol The Svedberg, Uppsala 1944, pages 311 319. The

stability constant of the complex of silver ion with acetonitrile: see F.G. Pawelka, Zeitschr. Elektrochemie 30, page 180 [1924]; the stability constant of the com plex of silver ion with allyl alcohol: see S. Winstein and HJ. Lucas, J.Am.Chem.Soc.60, page 836 [1938].

The stability constant K of the reaction Agni) where L-.represents the ligand concerned. For some suitable ligands the K-value in-(Liter/mole) is, for example,'as follows:-

Thiodiglycol Z-hydroxyethyl-rnethyls'ulphide 10 disodium salt of di-(p-sulphonyl)-sulphide lthiodiglycollic acid thiodipropionic acid l0 acetonitrile 10" allyl alcohol 10" pyrazine 1 0" The pH value of the treatment bath should advantageously be below 6. Acids suitable foradjusting the pH value are, for example, sulphamic acid, sulphuric acid, oxalic acid, citric acid, perchloric acid, nitric acid and other acids capable of forming readily soluble silver salts. When the salts of the oxidant, for example copper sulphate, form acid solutions'in water it is not necessary to add additional acid to the treatment bath.

The proportions of the individual constituents may be varied within wide limits. it is also possible to use mixtures containing more than one of each of the acids, oxidants and complexing agents. The bath may further contain conventional additives, such as surface-active- I colored image by diffuse light and second development 54, pages 264 276 [1958] andE. Larsson in the book or by development in the presence of a fogging agent, or by sulphidation. i

The invention is of special importance in carrying out the silver dye bleach-negative-positive process. In the usual silver dye bleaching process a material is used that contains photosensitive silver -halide and a dyestuff; On exposure and development a silver image is formed whose gradation is the opposite of that of the master (negative silver image). By decomposing the dyestuff on the silver a color gradation is achieved which is opposite to that of the silver image, that is to say equal to that of the master. Thus, a positive color image of a positive master is obtained.

To produce a positive color image from a negative master by the silver dye bleach process, a reversal f to metallic silver and then decomposing the dyestuff the metallic silver and the sparingly. soluble silver salt are contained in the same silver emulsion layer. This is the case whenever the metallic silver is distributed to form an image, especially inreversal processes where a primarily .developed silver image isdissolved and the residual silver salt image is converted into a black or depending on the amount of silver present in the layer, and removing the primary silver image by means of an acid bath which is free from anions that form sparingly soluble silver salts and which contains an oxidant and a complexing agent capable of forming with silver complexes of little stability;

When the acid and the oxidant to this invention, the bleachable dyestuff is not attacked and this makes the present process superior to the dichromate process. The superiority over the process according to German specification No. 1,154,347 is based on the fact that the present process requiresa smaller number of baths.

The temperature of the silverbleaching bath and the treatment time may be varied within wide limits without incurring a loss of undeveloped silver halide.

The present process is applicable to the treatment of both single-layer and multilayer color materials, of materials for viewing in incident light and transparencies, of mixed grain emulsion layers and of materials with incorporated capsules. Thus, for example, a rapid reversal process can be carried out with a metarial which contains acid, oxidant and complexing agents in crushable pods. Another variant starts from a material that contains oxidant and complexing agents in-pods which disintegrate only when they come into contact with an acid bath. I

The process according to the present invention is of special value in connection with reversal processes but the invention is also suitable for other processes in which metallic silver (such as developed image silver, latent image nuclei or colloidal silver) is dissolved without affecting any sparingly soluble silver salts present (which are present in the same grain, in the same layer or in another layer).

In the following Examples, which illustrate the invention, all percentages are percentages by weight.

EXAMPLE 1 Two strips of a blue-sensitized emulsion layer on a cellulose triacetate base, containing 0.7 g of silver bromide and 0.12 g of a yellow dyestuff of the formula are chosen according a nous n 5,0 11 per square meter, are exposed under a stepped wedge. The exposed strips are developed with a commercial para-methylaminophenol sulphate/hydroquinone developer and the development process is stopped with a 3 percent solution .of acetic acid. After having been washed in water for 1 minute, one strip is treated for 3 minutes'a'nd the other strip for 10 minutes with a solution'of thefollowing composition to remove the metallic silver left in the layer after the first development:

lron-lll-perchlorate nonahydrate 52 gsulphamic acid 60 g thiodiglycol l2.5 g water, to pH value: 0.35. 1 liter.

After having been rinsed in water for 4 minutes, the

strips are treated for 6 minutes with a commercial p-' methyl-aminophenol-sulphate/hydroquinone Hydrochloric acid, 37% strength 70 ml potassium bromide 50 g thiourea 80 g 2-amino-3-hydroxyphenazine 5 mg water, to l liter.

After 6 minutes immersion the strips are rinsed in water and treated with a silver bleaching bath of the following composition:

Potassium iron(lll)cyanide 75 g potassium bromide l5 g primary sodium phosphate monohydrate [0 g g sodium acetate trihydrate I 5 g glacial acetic acid l0 ml water, to Y l liter.

The strips are then rinsedin water for 1 minute and fixed with an acid'thio'sulphate solution in the known manner. Both strips'carry identical yellow images of the stepped wedge used for the exposure, which are negative with respect to the master.

EXAMPLE 2 The procedure used is as described in Example l, ex v cept that the metallic silver left after the first development is removed with a bath composed as follows:

lron(lll)perchlorate nonahydrate .28 g 2 N-nitric acid 50 ml Z-hydroxyethyl-methylsulphide 9.6 gv water, to l liter.

pH value: 0.65]

The? resulting pictures are Gil; SOalI EXAMPLE 3 Instead of the bath described in Example 2 a solution I of the following compositionis used.: I

Benzoquinone, dissolved in 200 ml of methanol l0.8 g ZN-sulphuric acid 50 ml 2-hydroxyethyl-methylsulphide l(l)|g iter water, to

pH value: 0.8

The resulting images are identical to those described in'Example l. p v

EXAMPLE 4 Instead of the bath described in Example 2 a solution of the following composition is usedr lron(lll)p crchlorate nonahydrate 52 g perchloric acid, strength 150 g disodium salt of di-(p-sulphophenyl)-sulphide g water, to 1 liter pH value: 0.6.

The resulting images'are identical to those of Example l. I

EXAMPLES instead of the bath described in Example 2 a solution of the following composition is used:

lron(lll)perchlorate nonahydrate 52 g thiodiglycolic acid 15 g uulphumic acid 60 g water. to I l liter pH value: 0.35.

The resulting images are identical to those of Exam- 'ple 1.

I EXAMPLE6 instead of the bath describedin Example 2 a solution of the following composition is used:

lron(lll)perchlorate nonahydrate 52 g thiodipropionic acid 18 g sulphamic acid 60 g water, to 1 liter pH value: 0.35.

described in Example I.

EXAMPLE 7.

instead of the bath'described in Example 2 a solution of the following composition'isused: a

lron(lll)perchlorate nonahydrate 52 g sulphamic'acid 60 g water, to 1 liter thiophene-2,5-dicarboxylic acid to saturation The resulting images are identical to those obtained A as described in Example 1.

pH value: 0.35

The-resultingimages areidentical to those of Examplel.

identical to those EXAMPLE 8 is exposedunder a grey wedge andthen processed as described in Example 1, except that the metallic silver left in the layer after the first development is removed with a bath of the following composition:

lnstead of the bath described in Example 2 a solution of the following composition is used:

5 lron(lll)perchlorate nonahydrate 52 g v sulpharmc acid 60 g lr0n(lll)perchlorate nonahydrate' 52 g acetonitrile I00 g oxalic acid dihydrate 40 g water, to l lltur thiodiglycol 12.5 g

- pH value: 0.35. water, to l liter pH value: 0.35.

The resulting images are identical to those described in Example 1.

. for the exposure IS a negative of the. master. Identical EXAMPLE 9 results are obtained in the 3-minutes and the 10 Instead of the bath described in Example 2 a solution minutes test l5 ofthe following composition 18 used:

EXAMPLE l2 lron(lll)pcrchlorate nonahydrate 52 g sulphflmw 8 A photographic tripack material which carried on a allyl alcohol 8 b l 1) I (l l water, to 20 transparent ase a red-sensitized Sl ver rorm eemu pH value: 0.35. sion containing acyan dyestuff as described in Example s 10, covered by a green-sensitized emulsion layer con- I The resulting images are ldem to those of EXamtaining a magenta dyestuff asdescribed in Example 1 l, P I which layer in turn is coveredby a blue-sensitized silver 1 EXAMPLE 10 bromide emulsion layer containingv a yel ow azo N=N.N= i Hogs S0311 (511.6

. dyestuff as described in Example 1,. is exposed under a -A red-sensitized emulsion layer which contains per grey wedge. Processing is carried out as described in square meter of cellulose triacetate base 0.7 gm of Example 1, except that the metallic silver left in the silver bromide and 0.1 15 g of a blue-green dyestuff of layer after the first development is removed with a bath the formula I of the following composition:

OuH

40 is exposed under a stepped wedge and then processed Copper(ll)sulphate pentahydrate 125 g as described in Example 1, except that the metallic sg g g Y i' g silver left in the layer after the first development is pH value:3.5. removed with a bath com osed as follows: I

p v A reproduction of the grey wedge used for the expolmnmngechloraw nonahydrate Y 52 g sure rs obtained which 15 a negative of the master. citric aci ihydrate 1 52 g thiodiglycol 12.8 g EXAMPLE 13 water, to 1 lit v I pH value: 0.5. A commercial enlarging paper, whose emulsion layer contains a silver halide consisting of 54 mol percent of A blue-green image of the stepped wedge used for silver chloride and 47 mol percent of silver bromide, is the exposure'is obtained which is negative with respect exposed under a grey wedge and then developed with a to the master. No differences can be noted by comparcommercial .merh l i h l ing the results ofthe 3-minutes test with those of the gulphate/hydroquinone ,developer. After having been lO-mmutes test. 5S rinsed in water for 2 minutes the paper is immersed in a solution of the followin com osition: EXAMPLE 1 1 g p g lron(lll)perchlorate nonahydrate 52 g A green-sensit zed emulsion layer which contains per lp i acid 2 square meter of a t'riacetate base 0.7 g of silver bromide sg'ig g g lter and 0.150 g ofa magenta dyestuff of the formula 6 pH value: 0.35.

(5) Hogs I soar The resulting magenta image of the grey wedge used After 8 minutes the paper is rinsed in water and then exposed in diffuse light.

The silver halide left in the layer is then reduced to metallic silver with the developer used in Example 1.

The resulting silver image of the grey wedge used for the exposure is a positive reproduction of the master.

EXAMPLE 14 A strip of an emulsion layer on an opaque cellulose triacetate base, sensitive to red light, which carries per square meter of base 0.7 g of silver bromide and 0.115 g of the cyan dyestuff of the formula (4) is exposed under a stepped wedge and then processed as described in Example l, except that the metallic silver left in the layer after the first development is removed with a bath of the following composition:

Ammonium-iron(lll)sulphate dodecahydrate 60 g 2N-sulphuric acid 100 ml pyrazine 50 g 1 liter water, to

- pH value: 0.8.

The resulting cyan-colored image is a negative of the stepped wedge used for the exposure.

EXAMPLE The process described in Example 14 is used, except that the metallic silver formed after the first development is removed with a bath of the following composition:

lron(lll)nitrate nonahydrate 40 g 2N-nitric acid 100 ml pyrazine 50 8 water, to 1 liter pH value: 0.8.

As in Example 14 a cyan-colored image is obtained which is a negative reproduction of the stepped wedge used for the exposure.

Iclaim: I

1. In a process for removing metallic silver without attacking any dyestuffs or sparingly soluble silver halides present from a photographic material comprising sparingly soluble silver halides and metallic silver distributed in at least one emulsion layer on a support by the steps of exposing, developing, reversal developing, dye bleaching, silver bleaching and fixing, the improvement which comprises treating said material after the I first silver image developing bath with an acid bath free from anions that form sparingly soluble silver halides, said bath containing an oxidant selected from a copper (ll) salt, a quinone or an iron (Ill) salt, and a complexing agent selected from allyl alcohol, a nitrile and a thio-ether.

2. A process as claimed in claim 1, wherein a watersoluble aliphatic monothioether is used as complexing agent.

3. A process as claimed in claim 1, wherein the complexing agent is a monothioether of the formula in which R, and R which may be the same or different, each represents alkyl having at most three carbon atoms, and X, and X which may be the same or different, each represents hydrogen or hydroxyl or carboxyl.

4. A process as claimed in claim 1, wherein the complexing agent is a monothioether of the formula mHx. S

in which X, and X which may be the same or different,

each represents hydrogen, hydroxyl or carboxyl.

5. A process as claimed in claim 1, wherein the silver 

1. In a process for removing metallic silver without attacking any dyestuffs or sparingly soluble silver halides present from a photographic material comprising sparingly soluble silver halides and metallic silver distributed in at least one emulsion layer on a support by the steps of exposing, developing, reversal developing, dye bleaching, silver bleaching and fixing, the improvement which comprises treating said material after the first silver image developing bath with an acid bath free from anions that form sparingly soluble silver halides, said bath containing an oxidant selected from a copper (II) salt, a quinone or an iron (III) salt, and a complexing agent selected from allyl alcohol, a nitrile and a thio-ether.
 2. A process as claimed in claim 1, wherein a water-soluble aliphatic monothioether is used as complexing agent.
 3. A process as claimed in claim 1, wherein the complexing agent is a monothioether of the formulaX1-R1-S-R2-X2 in which R1 and R2 which may be the same or different, each represents alkyl having at most three carbon atoms, and X1 and X2 which may be the same or different, each represents hydrogen or hydroxyl or carboxyl.
 4. A process as claimed in claim 1, wherein the complexing agent is a monothioether of the formula in which X1 and X2 which may be the same or different, each represents hydrogen, hydroxyl or carboxyl.
 5. A process as claimed in claim 1, wherein the silver halide is silver bromide.
 6. A process as claimed in claim 1, wherein the pH value of the bath is below
 6. 7. A process as claimed in claim 1, wherein the metallic silver and the silver halide are present in the same emulsion layer.
 8. A process as claimed in claim 1, carried out in a reversal development process. 